Know the 5 Kinds of Nucleotides

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Helmenstine, Anne Marie, Ph.D. "Know the 5 Kinds of Nucleotides." ThoughtCo, Oct. 3, 2017, thoughtco.com/know-the-kinds-of-nucleotides-4072796. Helmenstine, Anne Marie, Ph.D. (2017, October 3). Know the 5 Kinds of Nucleotides. Retrieved from https://www.thoughtco.com/know-the-kinds-of-nucleotides-4072796 Helmenstine, Anne Marie, Ph.D. "Know the 5 Kinds of Nucleotides." ThoughtCo. https://www.thoughtco.com/know-the-kinds-of-nucleotides-4072796 (accessed October 20, 2017).

How Many Kinds of Nucleotides Are There?

In DNA, there are four nucleotides: adenine, thymine, guanine, and cytosine. Uracil replaces thymine in RNA.
In DNA, there are four nucleotides: adenine, thymine, guanine, and cytosine. Uracil replaces thymine in RNA. Andrey Prokhorov / Getty Images

There are 5 nucleotides that are commonly used in biochemistry and genetics. Each nucleotide is a polymer made up of three parts:

  • A five carbon sugar (2'-deoxyribose in DNA or ribose in RNA)
  • A phosphate molecule
  • A nitrogenous (nitrogen-containing) base

Names of Nucleotides

The five bases are adenine, guanine, cytosine, thymine, and uracil, which have the symbols A, G, C, T, and U, respectively. The names of the bases are generally used as the names of the nucleotide, although this is technically incorrect. The bases combine with the sugar to make the nucleotide adenosine, guanosine, cytidine, thymidine, and uridine.

Nucleotides are named based on the number of phosphate residues they contain. For example, a nucleotide that has an adenine base and three phosphate residues would be named adenosine triphosphate (ATP). If the nucleotide has two phosphates, it would be adenosine diphosphate (ADP). If there is a single phosphate, the nucleotide is adenosine monophosphate (AMP).

More Than 5 Nucleotides

Although most people only learn the 5 main types of nucleotides, there are others. For example, there are cyclic nucleotides (e.g., 3'-5'-cyclic GMP and cyclic AMP). The bases may also be methylated to form different molecules.

Continue reading for information about how the parts of a nucleotide are connected, which bases are purines and pyrimidines, and a closer look at each of the 5 bases.

How the Parts of a Nucleotide Are Connected

The parts of a nucleotide are a nucleoside plus one or more phosphate groups.
The parts of a nucleotide are a nucleoside plus one or more phosphate groups. wikipedia.org

Both DNA and RNA use 4 bases, but they don't use the exact same ones. DNA uses adenine, thymine, guanine, and cytosine. RNA uses adenine, guanine, and cytosine, but has uracil instead of thymine. The helix of the molecules forms when two complementary bases form hydrogen bonds with each other. Adenine binds with thymine (A-T) in DNA and with uracil in RNA (A-U). Guanine and cytosine complement each other (G-C).

To form a nucleotide, a base connects to the first or primary carbon of ribose or deoxyribose. The number 5 carbon of the sugar connects to the oxygen of the phosphate group. In DNA or RNA molecules, a phosphate from one nucleotide forms a phosphodiester bond with the number 3 carbon in the next nucleotide sugar.

Adenine Base

Adenine molecule, where gray atoms are carbon, white are hydrogen, and blue are nitrogen.
Adenine molecule, where gray atoms are carbon, white are hydrogen, and blue are nitrogen. LAGUNA DESIGN / Getty Images

The bases take one of two forms. Purines consist of a double ring in which a 5-atom ring connects to a 6-atom ring. Pyrimidines are single six-atom rings.

The purines are adenine and guanine. The pyrimidines are cytosine, thymine, and uracil.

The chemical formula of adenine is C5H5N5. Adenine (A) binds to thymine (T) or uracil (U). It is an important base because it is used not only in DNA and RNA, but also for the energy carrier molecule ATP, the cofactor flavin adenine dinucleotide, and the cofactor nicotinamide adenine dincucleotide (NAD).

Adenine vs Adenosine

Remember, although people tend to refer to the nucleotides by the names of their bases, adenine and adenosine are not the same thing! Adenine is the name of the purine base. Adenosine is the larger nucleotide molecule made up of adenine, ribose or deoxyribose, and one or more phosphate groups.

Thymine Base

Thymine molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen.
Thymine molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen. LAGUNA DESIGN / Getty Images

The chemical formula of the pyrimidine thymine is C5H6N2O2. Its symbol is T and it is found in DNA but not RNA.

Guanine Base

Guanine molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen.
Guanine molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen. MOLEKUUL/SCIENCE PHOTO LIBRARY / Getty Images

 The chemical formula of the purine guanine is C5H5N5O. Guanine (G) only binds to cytosine (C). It does so in both DNA and RNA.

Cytosine Base

Cytosine molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen.
Cytosine molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen. LAGUNA DESIGN / Getty Images

The chemical formula of the pyrimidine cytosine is C4H5N3O. Its symbol is C. This base is found in both DNA and RNA. Cytidine triphosphate (CTP) is an enzyme cofactor that can convert ADP to ATP.

Cytosine can spontaneously change into uracil. If the mutation is not repaired, this can leave a uracil residue in DNA.

Uracil Base

Uracil molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen.
Uracil molecule, where gray atoms are carbon, white are hydrogen, red are oxygen, and blue are nitrogen. LAGUNA DESIGN / Getty Images

Uracil is a weak acid which has the chemical formula C4H4N2O2. Uracil (U) is found in RNA, where it binds with adenine (A). Uracil is the demethylated form of the base thymine. The molecule recycles itself through a set of phosphoribosyltransferase reaction.

One interesting factoid about uracil is that the Cassini mission to Saturn found that the moon Titan appears to have uracil on its surface.

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Helmenstine, Anne Marie, Ph.D. "Know the 5 Kinds of Nucleotides." ThoughtCo, Oct. 3, 2017, thoughtco.com/know-the-kinds-of-nucleotides-4072796. Helmenstine, Anne Marie, Ph.D. (2017, October 3). Know the 5 Kinds of Nucleotides. Retrieved from https://www.thoughtco.com/know-the-kinds-of-nucleotides-4072796 Helmenstine, Anne Marie, Ph.D. "Know the 5 Kinds of Nucleotides." ThoughtCo. https://www.thoughtco.com/know-the-kinds-of-nucleotides-4072796 (accessed October 20, 2017).